1. Field of the Invention
The present invention relates generally to a mobile communication system, and in particular, to an apparatus and method for transmitting and receiving serving high speed shared control channel (HS-SCCH) set information in a mobile communication system supporting a high speed downlink packet access (HSDPA) scheme.
2. Description of the Related Art
FIG. 1 schematically illustrates a structure of a general mobile communication system. Illustrated in FIG. 1 is a universal mobile terrestrial system (UMTS) mobile communication system, which is comprised of a core network (CN) 100, a plurality of radio network subsystems (RNSs) 110 and 120, and a user equipment (UE) 130. Each of the RNS 110 and RNS 120 is comprised of a radio network controller (RNC) and a plurality of Node Bs. For example, the RNS 110 is comprised of an RNC 111, a Node B 113 and a Node B 115, and the RNS 120 is comprised of an RNC 112, a Node B 114 and a Node B 116. Further, the RNC is classified into a serving RNC (SRNC), a drift RNC (DRNC) and a controlling RNC (CRNC) according to its operation. The SRNC refers to an RNC that manages information on each UE and controls data communication with the CN 100, and the DRNC refers to a drift RNC through which data from a UE is transmitted to the SRNC. The CRNC refers to an RNC which controls each of Node Bs. In FIG. 1, if information on the UE 130 is managed by the RNC 111, the RNC 111 serves as an SRNC for the UE 130, and if data of the UE 130 is transmitted and received through the RNC 112 as the UE 130 moves toward the RNC 112, the RNC 112 becomes a DRNC for the UE 130. Further, the RNC 111 that controls the Node B 113 in communication with the UE 130 becomes a CRNC of the Node B 113.
So far, a brief description of a UMTS mobile communication system has been made with reference to FIG. 1. Next, a mobile communication system supporting an HSDPA scheme (hereinafter, referred to as an “HSDPA mobile communication system”) will be described below.
Generally, the HSDPA scheme refers to a data transmission scheme including a high speed downlink shared channel (HS-DSCH), which is a downlink data channel for supporting high-speed transmission of downlink packet data in a UMTS mobile communication system, and its associated control channels. In order to support the HSDPA scheme, there have been proposed adaptive modulation and coding (AMC), and hybrid automatic retransmission request (HARQ). Commonly, in the HSDPA mobile communication system, the maximum number of orthogonal variable spreading factor (OVSF) codes that can be assigned to one UE is 15, and the system adaptively selects a modulation scheme of quadrature phase shift keying (QPSK), 16-ary quadrature amplitude modulation (16QAM) or 64-ary quadrature amplitude modulation (64QAM) according to channel conditions. The HSDPA mobile communication system performs retransmission on defective data between a UE and a Node B, and soft-combines the retransmitted data thereby improving entire communication efficiency. That is, a scheme for soft-combining the retransmitted data for the defective data is the HARQ scheme. Herein, a description will be made of an n-channel SAW (Stop And Wait) HARQ scheme, by way of example.
In a general automatic retransmission request (ARQ) scheme, acknowledgement (ACK) signals and retransmission packet data are exchanged between a UE and an RNC. However, in order to increase transmission efficiency of the ARQ scheme, the HARQ scheme proposes the following two plans. First, the HARQ scheme performs retransmission request and response between an UE and a Node B. Second, the HARQ scheme temporarily stores (buffers) defective data and then combines it with retransmission data of the corresponding data before transmission. Further, in the HARQ scheme, an ACK signal and retransmission packet data are exchanged between the UE and a medium access control (MAC) HS-DSCH of the Node B. In addition, the HSDPA scheme has introduced the n-channel SAW HARQ scheme that forms n logical channels to transmit several packet data blocks even though an ACK signal is not yet received . Unlike this, the existing SAW ARQ scheme transmits the next packet data only after receiving an ACK signal.
However, in some cases, the SAW ARQ scheme, since it transmits the next packet data only after receipt of an ACK signal, must undesirably wait for the ACK signal although it currently has the ability to transmit the next packet data. In contrast, the n-channel SAW HARQ continuously transmits a plurality of packet data blocks even before receipt of an ACK signal for the previous packet data, thereby increasing channel efficiency. That is, if n logical channels are set up between a UE and a Node B and the n logical channels can be identified by time or channel numbers, the UE receiving packet data can determine a channel over which packet data received at a certain time has been transmitted, and rearrange the received packet data blocks in right reception order or soft-combine corresponding packet data blocks.
In order to increase its efficiency compared with that of the SAW ARQ scheme, the n-channel SAW HARQ scheme has introduced the following two schemes.
In a first scheme, a receiver temporarily stores defective data and then soft-combines it with retransmission data of the corresponding data, thereby decreasing an error rate. The soft combining scheme includes a chase combining (CC) scheme and an incremental redundancy (IR) scheme. In the CC scheme, a transmitter uses the same format at both initial transmission and retransmission. If m symbols were transmitted over one coded block at initial transmission, m symbols are transmitted over one coded block even at retransmission. That is, the same coding rate is applied to both initial transmission and retransmission during data transmission. Therefore, the receiver combines an initially transmitted coded block with a retransmitted coded block, and performs a cyclic redundancy check (CRC) operation on the combined coded block, to determine whether the combined coded block is defective.
Next, the IR scheme uses different formats at initial transmission and retransmission. For example, if n-bit user data is generated into m symbols through channel coding, a transmitter transmits only some of the m symbols at initial transmission, and then sequentially transmits the remaining symbols at retransmission. That is, a coding rate for initial transmission is different from a coding rate for retransmission during data transmission. Therefore, a receiver forms a coded block with a high coding rate by adding retransmitted coded blocks to the remaining blocks of the initially transmitted coded block, and then performs error correction on the formed coded block. In the IR scheme, the initially transmitted coded blocks and the retransmitted coded blocks are identified by redundancy versions (RVs). For example, an initially transmitted coded block is identified by RV#1, a first retransmitted coded block by RV#2, and a second retransmitted coded block by RV#3, and the receiver can correctly combine the initially transmitted coded block with the retransmitted coded blocks, using the RV information.
A second scheme introduced to increase efficiency of the general SAW ARQ scheme will be described below. Although the general SAW ARQ scheme can transmit the next packet only after receipt of an ACK signal for a previous packet, the n-channel SAW HARQ scheme continuously transmits a plurality of packets even before receipt of an ACK signal, thereby increasing utilization efficiency of a radio link. In the n-channel SAW HARQ scheme, if n logical channels are set up between a UE and a Node B and the logical channels are identified by specified channel numbers, the UE being a receiver can determine a channel to which a packet received at a certain time belongs, and rearrange received packets in right reception order or soft-combine corresponding packets.
An operation of the n-channel SAW HARQ scheme will now be described in detail with reference to FIG. 1. It will be assumed herein that a 4-channel SAW HARQ scheme is performed between a UE 130 and a Node B 115 and respective channels are assigned logical identifiers of #1 to #4. Further, physical layers of the UE 130 and Node B 115 have HARQ processors associated with the corresponding channels. The Node B 115 assigns a channel identifier #1 to an initially transmitted coded block and transmits it to the UE 130. The “coded block” means user data transmitted for one transmission time interval (TTI). If an error is generated in a corresponding coded block, the UE 130 transmits the coded block to an HARQ processor #1 associated with a channel #1 based on the channel identifier, and transmits a negative acknowledgement (NACK) signal for the channel #1 to the Node B 115. The Node B 115 then can transmit the next coded block over a channel #2 regardless of arrival of an ACK signal for the coded block on the channel #1. If an error is generated even in the next coded block, the UE 130 transmits the coded block as well to a corresponding HARQ processor. Upon receiving a NACK signal for the coded block on the channel #1 from the UE 130, the Node B 115 retransmits the corresponding coded block over the channel #1, and the UE 130 transmits the coded block to the HARQ processor #1 based on a channel identifier of the coded block. The HARQ processor #1 soft-combines the retransmitted coded block with the previously stored coded block. In this manner, the n-channel SAW HARQ scheme matches channel identifiers with HARQ processors on a one-to-one basis in order to properly match initially transmitted coded blocks with retransmitted coded blocks without delaying transmission of user data until receipt of an ACK signal.
Further, in the HSDPA communication system, a plurality of UEs can simultaneously use a plurality of available OVSF codes at a certain time. That is, in the HSDPA communication system, OVSF code multiplexing can be simultaneously performed between a plurality of UEs at a certain time. The OVSF code multiplexing will be described with reference to FIG. 2.
FIG. 2 illustrates an example of a method for assigning OVSF codes in a general HSDPA communication system. The OVSF code assignment method of FIG. 2 will be described with reference to a case where a spreading factor (SF) is 16 (SF=16).
Referring to FIG. 2, OVSF codes are represented by C(i,j) according to positions in a code tree. In the C(i,j), a parameter ‘i’ represents the SF value, and a parameter ‘j’ represents a position of an OVSF code starting from the leftmost side of the OVSF code tree. For example, C(16,0) represents an OVSF code with SF=16 located in a first position starting from the leftmost side of the OVSF code tree. FIG. 2 illustrates a method of assigning to the HSDPA communication system 16 OVSF codes of C(16,0) to C(16,15), i.e., the 0th to 15th OVSF codes in the OVSF code tree for the SF=16. The 16 OVSF codes can be multiplexed to a plurality of UEs in a manner illustrated in Table 1 by way of example.
TABLE 1ABCt0C(16, 0)~C(16, 5)C(16, 6)~C(16, 10)C(16, 11)~C(16, 14)t1C(16, 0)~C(16, 3)C(16, 4)~C(16, 14)—t2C(16, 0)~C(16, 3)C(16, 4)~C(16, 5)  C(16, 6)~C(16, 14)
In Table 1, A, B and C represent users or UEs using the HSDPA communication system. As illustrated in Table 1, at certain time points t0, t1 and t2, the users A, B and C are code-multiplexed using OVSF codes assigned to the HSDPA communication system. The number of OVSF codes assigned to the UEs and positions of the OVSF codes in the OVSF code tree are determined by a Node B considering an amount of user data of each UE stored in the Node B and conditions of channels set up between the Node B and the UEs.
That is, in the HSDPA communication system, control information exchanged between a UE and a Node B includes the number of OVSF codes to be used by a particular UE, code information designating positions of the OVSF codes in the code tree, channel quality information necessary for adaptively determining a modulation scheme according to channel conditions, an MCS level (or modulation scheme information), channel number information necessary for supporting the n-channel SAW HARQ scheme, and ACK/NACK information. A description will now be made of control information transmitted and received in the HSDPA communication system, and channels used to transmit actual user data.
First, channels used in the HSDPA communication system are divided into a downlink (DL) channel and an uplink (UL) channel as follows. The downlink channel includes a high speed shared control channel (HS-SCCH), an associated dedicated physical channel (DPCH) and a high speed physical downlink shared channel (HS-PDSCH), and the uplink channel includes a secondary DPCH.
A relationship between the downlink channels and the uplink channel will be described with reference to FIG. 3.
FIG. 3 illustrates downlink and uplink channels in a general HSDPA communication system. Referring to FIG. 3, a UE first measures channel quality between the UE itself and a Node B using a primary common pilot channel (PCPICH) signal (not shown), and reports the measured channel quality to the Node B through a channel quality report (CQR). The CQR is transmitted over a secondary DPCH. Since a method of transmitting CQR from the UE to the Node B is not directly related to the present invention, a detailed description thereof will not be provided.
Upon receiving CQR from the UE, the Node B performs scheduling based on the received CQR. The “scheduling” means selecting a UE expected to receive actual data at the next TTI among a plurality of UEs, and then determining a modulation scheme to be used for transmission of the data and the number of codes to be assigned to the UE. After selecting a UE expected to transmit data at the next TTI through the scheduling, the Node B transmits an HS-DSCH indicator (HI) over an associated DPCH set up between the selected UE and the Node B. The HI indicates a UE to which data transmitted over HS-PDSCH will be transmitted, and includes an identifier indicating the HS-SCCH for transmitting actual control information necessary for receiving the data. For example, in the case where 4 HS-SCCHs are set up to the Node B and the HI is comprised of 2 bits, the 4 HS-SCCHs are indicated by HI of 00, 01, 10 and 11. If no information is transmitted through the HI, it means that no data will be transmitted to a corresponding UE at the next TTI. A set of HS-SCCHs assigned to a particular UE will be defined as a “serving HS-SCCH set”. The serving HS-SCCH set can be individually set for each of the UEs, and a detailed description thereof will be made later.
Further, while transmitting the HI, the Node B transmits control information necessary for receiving corresponding data at a corresponding UE, over a corresponding HS-SCCH. The control information transmitted over the HS-SCCH will now be described with reference to FIG. 4.
FIG. 4 illustrates an HS-SCCH structure in a general HSDPA communication system. Referring to FIG. 4, a slot format of the HS-SCCH is comprised of a part#1 field 411, a CRC#1 field 413, a part#2 field 415, and a CRC#2 field 417. Further, control information transmitted over the HS-SCCH includes:                1) HS-DSCH channelization code information (hereinafter, referred to as “code_info”)        2) modulation scheme (MS) information        3) transport block size (TBS) information        4) transport channel identifier (TrCH ID) information        5) UE specific CRC information        6) HARQ channel number information        7) new data indicator (NDI) information        8) RV information        
Among the control information transmitted over the HS-SCCH, the MS information, TBS information, and code_info information will be referred to as “transport format and resource related information (TFRI),” and the HARQ channel number information, RV information, and NDI information will be referred to as “HARQ information.” Further, when the HS-SCCH is transmitted using an OVSF code with SF=128, each of the control information assigns 1 bit for the MS information, 7 bits for the code_info information, 6 bits for the TBS information, 1 bit for the NDI information, 2 bits for RV information, and 3 bits for the HARQ channel number information, as illustrated in FIG. 4.
Referring to FIG. 4, the part#1 field 411 includes the code_info information and the MS information representing positions and the number of OVSF codes in a code tree, to be used by a corresponding UE, and the CRC#1 field 413 includes the information included in the part#1 field 411 and CRC operation results for a UE identifier (UE ID). It is expected that 10 bits will be assigned for the UE identifier. Although the UE identifier is not actually transmitted, a transmitter calculates the UE identifier while calculating CRC#1, and a receiver also calculates the UE identifier while calculating CRC#1. By calculating CRC#1 using the UE identifier in this way, a UE can determine whether control information included in a particular HS-SCCH is control information corresponding to the UE itself. For example, when transmitting control information to a first UE over HS-SCCH, a Node B calculates CRC#1 based on information included in the part#1 field 411 and an UE identifier of the first UE. Therefore, the first UE determines, as control information for the first UE itself, control information included in particular HS-SCCH of which CRC#1 has no error when its UE identifier and information included in the part#1 field 411 are calculated together, among HS-SCCHs belonging to its serving HS-SCCH set. In addition, the part#2 field 415 includes the TBS information which indicates a size of data transmitted over HS-PDSCH, the HARQ channel number information, the NDI information indicating whether data transmitted over the HS-PDSCH is new data or retransmission data, and the RV information representing a version number of the corresponding data in the IR scheme. Further, CRC operation results for information included in the part#2 field 415 is transmitted through the CRC#2 field 417.
The code_info information will now be described with reference to FIG. 5.
FIG. 5 schematically illustrates a method of matching code_info of HS-DSCH to logical identifiers in an HSDPA communication system. Referring to FIG. 5, as stated above, when HS-SCCH signal is transmitted using an SF=128 OVSF code, 7 bits are assigned for code_info. Therefore, the logical identifiers are assigned by separating the 7 bits into a first 3 bits and a remaining 4 bits. For example, a logical identifier for which the first 3 bits of the code_info is 6 (110) and the remaining 4 bits is 4 (0011) is [m=7, SP(Start Point)=4]. That is, a logical identifier ‘110 0011’ means 7 OVSF codes starting from a 4th OVSF code in an OVSF code tree, i.e., OVSF codes of C(16,3) to C(16,9). As illustrated in FIG. 5, when 7 bits are assigned to the code_info, 8 logical identifiers of “111 0000”, “111 0001”, “111 0010”, “111 0011”, “111 0100”, “111 0101”, “111 0110”, and “111 1111” are not used.
Now, a process of actually receiving data by a UE based on the control information transmitted over the HS-SCCH will be described below.
A UE receives data transmitted over HS-PDSCH and demodulates the received data based on control information received over HS-SCCH. The UE determines an OVSF code with which it will receive and demodulate HS-PDSCH, based on the code_info, and determines a modulation scheme based on the MS information. Thereafter, the UE determines whether the received data has an error, through a CRC operation. As a result of the determination, if no error has occurred in the receive data, the UE transmits an ACK signal, and if a error has occurred, the UE transmits a NACK signal. Actual user data transmitted over the HS-PDSCH will be defined as a “medium access control-high speed (MAC-hs) protocol data unit (PDU)”.
A structure of the MAC-hs will now be described below with reference to FIG. 6.
FIG. 6 illustrates a structure of MAC-hs PDU transmitted over HS-PDSCH. Referring to FIG. 6, the MAC-hs PDU is comprised of a MAC-hs header field 611, a MAC-bs service data unit (SDU) field 613, and a CRC field 615. The MAC-hs header 611 includes such information as:
(1) Priority: this is a priority queue identifier of MAC-hs SDU 613, and 3 bits are assigned thereto.
(2) TSN (Transmission Sequence Number): this is a sequence number used when MAC-hs SDU 613 is reordered in a priority queue, and 5 or 6 bits are assigned thereto.
(3) SID_x: this represents a size of MAC-dedicated (MAC-d) PDUs belonging to an xth MAC-d PDU set among sets of PDUs constituting MAC-hs SDU 613, and 2 or 3 bits are assigned thereto.
(4) N_x: this represents the number of MAC-d PDUs belonging to an xth MAC-d PDU set, and 7 bits are assigned thereto.
(5) F (Flag): when F is set to 1, it means that the next field is a MAC-hs SDU field, and when F is set to 0, it means that the next field is an SID field. 1 bit is assigned thereto.
(6) MAC-d PDU_Nx: this represents MAC-d PDUs constituting an xth MAC-d PDU set.
As illustrated in FIG. 6, one MAC-hs SDU is comprised of several kinds of MAC-d PDUs. Before a description of the TSN, priority queue, and MAC-d PDU, a protocol stack of the HSDPA communication system will be described with reference to FIG. 7.
FIG. 7 illustrates a structure of a MAC layer in a general HSDPA communication system. Referring to FIG. 7, the MAC layer is comprised of a MAC-d layer and a MAC-hs layer, and as illustrated, a MAC layer of a UE includes a MAC-d- layer 711 and a MAC-hs layer 710, a Node B includes a MAC-hs layer 707, and an SRNC includes a MAC-d layer 702. The MAC-d layer, a MAC entity for dedicated channels, performs a MAC function on dedicated logical channels such as a dedicated control channel (DCCH) and a dedicated traffic channel (DTCH). Further, the MAC-hs layer, a layer additionally realized to support HSDPA, has a major function of supporting an HARQ scheme on HS-DSCH in order to support the HSDPA scheme.
In FIG. 7, if actual user data is transmitted from an upper layer 701 to a MAC-d layer 702 of an SRNC, the MAC-d layer 702 generates the user data delivered from the upper layer 701 into MAC-d PDUs, and delivers the generated MAC-d PDUs to a frame protocol (FP) layer 703. The MAC-d PDU is user data delivered from the upper layer 701, to which a MAC-d header is added, and the MAC-d header includes multiplexing-related information indicating an upper layer to which a receiver should transmit MAC-d PDUs. The FP layer 703 generates the MAC-d PDUs delivered from the MAC-d layer 702 into FP PDUs, and delivers the generated FP PDUs to a transport bearer layer 704. The FP layer 703 concatenates a plurality of MAC-d PDUs into one FP PDU, and the FP PDU includes priority information of the concatenated MAC-d PDUs. The transport bearer layer 704 assigns a transport bearer to the FP PDUs delivered from the FP layer 703, and interfaces the FP PDUs between the transport bearer layer 704 and a transport bearer layer 705 of a Node B through a lub interface, an interface between the SRNC and the Node B, through the assigned transport bearer. In addition, the transport bearer layer 704 is a part for controlling actual data transmission between the SRNC and the Node B, and can consist of AAL2 (Adaptive ATM Layer 2)/ATM (Asynchronous Transfer Mode).
Upon receiving the FP PDU from the SRNC transport bearer layer 704, the transport bearer layer 705 of the Node B delivers the received FP PDU to an FP layer 706, and the FP layer 706 delivers the FP PDU delivered from the transport bearer layer 705 to a MAC-hs layer 707. The MAC-hs layer 707 stores received MAC-d PDUs in a corresponding priority queue by consulting priority information included in the FP PDU delivered from the FP layer 706.
A structure of the MAC-hs layer for the Node B will now be described with reference to FIG. 8.
FIG. 8 illustrates a structure of a MAC-hs layer for a Node B in a general HSDPA communication system. Referring to FIG. 8, the Node B MAC-hs layer 707 has a function of processing a data block through HS-DSCH, and manages physical channel resources for the HSDPA data. That is, the MAC-hs layer 707 is comprised of a scheduling/priority handling part 805, a HARQ process part 803, and a TFRC selection part 804. The scheduling/priority handling part 805 performs scheduling and priority management on HS-DSCH, the HARQ process part 803 performs hybrid retransmission on received data blocks, and the TFRC selection part 804 selects a transport format resource combination (TFRC) for a shared transport channel. The TFRC selector 804 selects a proper modulation scheme by consulting the quality of a channel transmitted by a UE over a secondary DPCH, and delivers the selected modulation scheme information to a physical layer 708. The scheduling/priority handing part 805 has two priority queue distributors 801 and a plurality of priority queues 802 distributed by the priority queue distributor 801, per MAC-d flow.
The priority queue distributor 801 delivers the MAC-d PDUs delivered from the upper layer to a corresponding priority queue 802, based on priority information of the FP PDU delivered from the FP layer 706. One or more MAC-d multiplexers may exist between a UE and an SRNC, and one MAC-d flow is generated per MAC-d multiplexer. A detailed description of the MAC-d flow will be made later with reference to FIG. 10. MAC-d PDUs stored in the priority queue 802 are delivered to the HARQ processor 803 in response to a command from the scheduling/priority handling part 805. The HARQ processor 803 concatenates MAC-d PDUs delivered from the priority queue 802, generates a MAC-hs PDU by inserting a MAC-hs header 611 and a CRC 615 described in conjunction with FIG. 6 into the concatenated MAC-d PDUs, performs an n-channel SAW HARQ operation on the generated MAC-hs PDU, and then delivers the MAC-hs PDU to the physical layer 708. Further, the Node B MAC-hs layer 707 is directly connected to the physical layer 708, and has associated uplink/downlink signaling radio control channels for transmitting and receiving HSDPA-related control information to/from a UE through the physical layer 708.
Up to the present, a structure of the Node B MAC-hs layer 707 has been described. Next, a structure of the UE MAC-hs layer 710 will be described with reference to FIG. 9.
FIG. 9 illustrates a structure of a UE MAC-hs layer in a general HSDPA communication system. Referring to FIG. 9, the UE MAC-hs layer 710 also has a major function of supporting an HARQ scheme on HS-DSCH in order to support HSDPA. The MAC-hs layer 710 checks an error of a data block received from the Node B physical layer (PHY) 708, i.e., a radio channel. As a result of the error check, upon failure to detect an error generated for the received data block, or received packet data, the MAC-hs layer 710 transmits an ACK signal to the Node B physical layer 708. However, upon detecting an error for the data block, the MAC-hs layer 710 generates a NACK signal for requesting retransmission of the defective data block and transmits the generated NACK signal to the Node B physical layer 708. In addition, the MAC-hs layer 710 has radio control channels for associated uplink/downlink signaling in order to transmit and receive HSDPA-related control information to/from a UMTS terrestrial radio access network (UTRAN).
As illustrated in FIG. 9, the MAC-hs layer 710 is comprised of an HARQ processor 901, two reordering queue distributors 902, a reordering queue 903 and a de-assembler 904. The MAC-hs layer 710 can control an operation of a physical layer 709 depending on HARQ-related information on HS-SCCH, and a MAC-hs PDU is delivered from the reordering queue distributor 902 to a proper reordering queue 903. The reordering queue distributor 902 uses priority included in a priority field of a MAC-hs header in the received MAC-hs PDU. The ordering queue 903 reorders the order of received MAC-hs SDUs based on a value included in a TSN field of the MAC-hs PDU header, and delivers the reordered MAC-hs SDUs to the de-assembler 904. The de-assembler 904 de-assembles MAC-hs SDU into MAC-hs PDUs depending on SID_x field and N_x field of the MAC-hs header, and delivers the de-assembled MAC-hs PDUs to an upper layer 712.
Next, a structure of the above stated MAC-d multiplexer will be described with reference to FIG. 10.
FIG. 10 schematically illustrates a structure of a MAC-d multiplexer in a general HSDPA communication system. Referring to FIG. 10, a plurality of logical channels delivered from the upper layer 701 are multiplexed by one MAC-d multiplexer. The logical channel means a channel formed between a radio link control (RLC) layer, being an upper layer of a MAC layer, and the MAC layer, and one or two logical channels can be formed per RLC layer entity. The RLC layer entity matches data delivered from the upper layer to a predetermined size, and adds a header with a sequence number to the size-matched data. Since the RLC layer entity is not closely related to the present invention, a detailed description thereof will not be provided.
It is assumed in FIG. 10 that the MAC-d layer 702 includes 3 MAC-d multiplexer 1003, 1004 and 1005, and the MAC-hs layer 707 includes one MAC-d multiplexer 1006. For the convenience of explanation, a description will be made of only the MAC-d multiplexer 1003 among the MAC-d multiplexers 1003, 1004 and 1005. The MAC-d multiplexer 1003 multiplexes a plurality of logical channels in such a manner that identifiers of logical channels are inserted in a C/T field (not shown) of a MAC-d header. The C/T field, information inserted in a header of a MAC-d PDU, is information used to identify logical channels multiplexed to one MAC-d. For example, assuming that an identifier of a logical channel 1001 is 0 and an identifier of a logical channel 1002 is 1, the MAC-d multiplexer 1003 inserts 0 and 1 in the C/T fields of MAC-d PDUs delivered by the corresponding logical channels so that a receiver can deliver the MAC-d PDUs over corresponding logical channels.
As described in conjunction with FIG. 10, since there exist a plurality of MAC-d multiplexers, logical channels having the same identifier, associated with different MAC-d multiplexers, are different logical channels, although they have the same logical channel identifier. For example, a logical channel with a logical channel identifier 0, connected to the MAC-d multiplexer 1003, and a logical channel with a logical channel identifier 0, connected to the MAC-d multiplexer 1004, are different logical channels, since they are connected to the different MAC-d multiplexers although they have the same logical channel identifier 0. Meanwhile, MAC-d PDUs multiplexed by the same MAC-d multiplexer constitute one MAC-d flow, and the MAC-d flow is delivered to the MAC-hs layer 707 via a lub interface.
Now, a detailed description of the serving HS-SCCH set will be made below.
The serving HS-SCCH set, as described above, means a set of HS-SCCHs that must be continuously monitored by a particular UE, and in the HSDPA communication system, the serving HS-SCCH set may include a maximum of 4 HS-SCCHs. That is, a plurality of HS-SCCHs are set up to one Node B, and a serving HS-SCCH set for a particular UE is comprised of some of the HS-SCCHs. For example, if a total of 8 OVSF codes of C(128,0) to C(128,7) are assigned to HS-SCCHs in a Node B#1, UEs receiving an HSDPA service within the Node B#1 will be assigned some of the HS-SCCHs as its serving HS-SCCH set. A signaling flow currently considered to inform a UE of the serving HS-SCCH set will now be described with reference to FIG. 11.
FIG. 11 is a signaling flow diagram illustrating a process of transmitting a serving HS-SCCH set in a general HSDPA communication system. Specifically, FIG. 11 illustrates a signaling flow for setting up an HSDPA call among UE, Node B, RNC and CN. In FIG. 11, ellipses mean protocol entities for transmitting and receiving messages. The types of information that must be included in the messages are illustrated in Table 2 below. For the sake of convenience, Table 2 illustrates only the information elements (IEs) that should be newly added or modified for the HSDPA. In addition, Reference of Table 2 represents reference documents where a full list of the corresponding IE can be acquired.
TABLE 2MessageReference501 RRC CONNECTION REQUEST3GPP TS 25.331.v4.1.0 ch 10.2.40502 RRC CONNECTION SETUP3GPP TS 25.331.v4.1.0 ch 10.2.41503 RRC CONNECTION SETUP COMPLETE3GPP TS 25.331.v4.1.0 ch 10.2.42504 INITIAL DIRECT TRANSFER3GPP TS 25.331.v4.1.0 ch 10.2.12505 INITIAL UE MESSAGE3GPP TS 25.413.v4.1.0 ch 9.1.33506 RAB ASSIGNMENT REQUEST3GPP TS 25.413.v4.1.0 ch 9.1.3507 RADIO LINK SETUP REQUEST3GPP TS 25.433.v4.1.0 ch 9.1.36508 RADIO LINK SETUP RESPONSE3GPP TS 25.433.v4.1.0 ch 9.1.37509 RADIO BEARER SETUP3GPP TS 25.331.v4.1.0 ch 10.2.31510 RADIO BEARER SETUP COMPLETE3GPP TS 25.331.v4.1.0 ch 10.2.32511 RAB ASSIGNMENT RESPONSE3GPP TS 25.413.v4.1.0 ch 9.1.4
Now, a process of transmitting the serving HS-SCCH set by the UE after setting an HSDPA call will be described with reference to FIG. 11 and Table 2.
A UE, as it enters a region of a Node B, acquires necessary system information (SI) through a cell selection process, and then transmits a radio resource control (RRC) Connection Request message to an RNC (Step 1101). The cell selection process means a process of matching synchronization to a corresponding cell using a common pilot channel (CPICH) and a primary common control channel (PCCPCH), and then acquiring random access channel (RACH) information. The RRC Connection Request message has a UE identity IE inserted therein so that the RNC can determine whether to set up RRC connection to a corresponding UE. The RRC connection means signaling connection through which the UE can initially access the system and transmit necessary information to a network. However, in some cases, a dedicated channel (DCH) for transmitting user data is included in the RRC connection. It will be assumed in FIG. 11 that the RRC Connection Request message requests only signaling connection setup.
Upon receiving the RRC Connection Request message, the RNC determines whether to approve RRC connection to the corresponding UE, using a UE identify IE, and transmits an RRC Connection Setup message with several RRC connection-related IEs to the UE if it has determined to permit RRC connection (Step 1102). The RRC Connection Setup message includes a UE identifier that the UE will use in common channels such as RACH and forward access channel (FACH). Upon receiving the RRC Connection Setup message, the UE transmits an RRC Connection Setup Complete message to the RNC along with a UE radio access capability IE (Step 1103). Commonly, the UE radio access capability IE includes a physical channel capability IE and an a physical channel capability IE representing whether a corresponding UE supports turbo coding. In the present invention, the UE radio access capability IE includes information indicating whether a corresponding UE supports HS-PDSCH reception. In addition, the RRC Connection Setup Complete message includes information indicating whether the UE supports a handover between different frequencies, i.e., “inter-frequency handover (HO).” Upon receiving the RRC Connection Setup Complete message, the RNC stores the UE-related information.
After setting up RRC connection as described above, the UE transmits, when necessary, an Initial Direct Transfer message for requesting new call setup to the RNC (Step 1104). The Initial Direct Transfer message used by the UE to transmit a new call setup request to the CN is included in a NAS (Non-Access Stratum) message IE of an RRC message. The NAS message may include information needed by the CN to process a corresponding call, e.g., call quality information. Therefore, as the UE transmits an Initial Direct Transfer message to the RNC, the RNC modifies the Initial Direct Transfer message into a RANAP message, called an “Initial UE message,” and transmits the Initial UE message to the CN (Step 1105). Upon receiving the Initial UE message, the CN determines a radio access bearer (RAB) parameter based on quality-related information of the NAS message IE included in the received Initial UE message. The RAB parameter includes a maximum bit rate of a corresponding call, a guaranteed bit rate, and a traffic class indicating a type of the call. The traffic class includes a conversational class, a streaming class, an interactive class and a background class. The conversational class and the streaming class have a real time feature, and typically correspond to a multimedia service including voice communication, and the interactive class and the background class have a non-real time feature and typically correspond to a data service. Therefore, if a call requested by the UE in Steps 1104 and 1105 is a data service, the CN will employ the interactive or background class to the RAB parameter, and if the call is a voice service, the CN will employ the conversation class to the RAB parameter. After determining the RAB parameter, the CN transmits a RAB Assignment Request message to the RNC (Step 1106). The RNC then determines a channel to be set up to the corresponding UE based on the RAB parameter included in the received RAB Assignment Request message. If the RAB parameter indicates that a call to be set up is a high-speed data service, i.e., a traffic class of the RAB parameter is an interactive or background class with a maximum bit rate, the RNC can set up the call as an HSDPA call.
Upon receiving the RAB Assignment Request message, the RNC transmits a Radio Link Setup Request message to a Node B that controls the corresponding cell (Step 1107). In the present invention, an HS-DSCH info IE is newly defined in the Radio Link Setup Request message, and the HS-DSCH info IE includes a UE identifier and other UE-related information. In addition, the Radio Link Setup Request message must include the associated DPCH and secondary DPCH-related information as well. The DPCH-related information may become an OVSF code, and may include activation point-related information indicating when the DPCHs will be activated. Upon receiving the Radio Link Setup Request message, the Node B stores a UE identifier included in the received Radio Link Setup Request message, assigns a buffer for servicing a corresponding UE, and forms a MAC-hs entity. Further, the Node B determines a serving HS-SCCH set of the corresponding UE. After completion of forming the DPCHs, the Node B transmits a Radio Link Setup Response message to the RNC (Step 1108). Upon receiving the Radio Link Setup Response message, the RNC transmits a Radio Bearer Setup message to the UE (Step 1109). The Radio Bearer Setup message includes the DPCH-related information and information that the UE must recognize in relation to HSDPA, i.e., the number of HARQ processors and serving HS-SCCH set-related information. Upon receiving the Radio Bearer Setup message, the UE transmits a Radio Bearer Setup Complete message to the RNC after forming DPCHs, in order to inform that it is ready to receive HS-PDSCH (Step 1110). The RNC then transmits a RAB Assignment Response message to the CN in order to inform completion of call setup (Step 1111).
The serving HS-SCCH set can be adaptively established by the Node B according to conditions of UEs receiving an HSDPA service. For example, if the number of UEs receiving an HSDPA service within one Node B is increased, it is possible to assign new OVSF codes to HS-SCCH, and as the new OVSF codes are assigned to the HS-SCCH, a serving HS-SCCH set of the UEs is reset. However, since the serving HS-SCCH set is information corresponding to each of the UEs and is information shared by a Node B and a UE, it is inefficient to transmit and receive the serving HS-SCCH set through an upper layer, i.e., SRNC. Accordingly, there have been demands for a method of resetting a serving HS-SCCH set for the UE for which the serving HS-SCCH set was initially established.